In the field of dental treatment, it is a widespread practice to shoot a panoramic image covering an entire area of a tooth portion at the start of treatment. In so doing, not only the tooth portion, but also the upper and lower jawbones are photographed. In recent years, of the shot images, images of a lower jawbone portion have come to be used to support osteoporotic diagnosis.
For example, Patent Literature 1 discloses a technical idea of supporting osteoporotic diagnosis by semiautomatically determining from a dental panoramic image whether an inner surface of a cortical bone portion of the lower jawbone is structured smoothly or coarsely.
Also, Patent Literature 2 discloses a technical idea of supporting osteoporotic diagnosis by measuring a thickness of a cortical bone portion of the lower jawbone from a dental panoramic image and comparing the thickness of the cortical bone with data accumulated in an osteoporosis database.
Also, Patent Literature 3 discloses a technical idea of supporting osteoporotic diagnosis by detecting a mandibular contour in a dental panoramic image and comparing a thickness of the mandibular cortical bone, in particular, with stored contour model data.
Furthermore, Non Patent Literature 1 discloses a technique for automatically measuring a thickness of the mandibular cortical bone using a dental panoramic image, and more particularly, a technical idea of acquiring a gray value profile of perpendicular lines from a mandibular contour and measuring the thickness of the mandibular cortical bone based on the mandibular contour.
Also, Patent Literature 4 discloses a technical idea of supporting osteoporotic diagnosis by automatically identifying an area where there is a change in bone density using a dental panoramic X-ray image.